1. Field of the Invention
The present invention relates to a method to prepare micro/nano hybrid hydrophobic/oleophobic polymer woven fabric surface and the hydrophobic/oleophobic surface prepared by the method.
More particularly, the present invention a method to prepare micro/nano hybrid hydrophobic/oleophobic polymer woven fabric surface artificially which has much lower wettability, variable contact angle to oil and great contact angle to pure water and the hydrophobic/oleophobic woven fabric surface prepared by the method.
2. Background of the Invention
In general, it is known that wettability of a solid surface depends on chemical features of the surface, but when minute pattern is formed on the solid surface, its wettability increase or decrease remarkably, so its hydrophilicity and hydrophobicity is improved. For example, when minute pillar or pore structures are formed on a flat surface with same chemical composition, the surface shows a trend that when its contact angle to pure water (an angle between fluid and solid equilibrating hydromechanically on the solid surface) is less than 90 degree, it decreases further and when the angle is more than 90 degree, it increases further. Thus, in case of hydrophobicity (contact angle>90 degree), existing 150 degree may increase to 170 degree, showing superhydrophobicity. Accordingly, wettability of the surface decreases remarkably.
For the theory about contact angle of a pure water drop on a fine pillar or pore formed hydrophobic surface, namely a surface with roughness, 2 models are known. One is a model with completely wet area under the water drop supposed by Wenzel [R. N. Wenzel, Ind. Eng. Chem. 28(1936)988], which is a theory that the roughness on the surface results in increase of apparent contact angle by increasing contact area between solid and water drop (fluid). The other one is a theory supposed by Cassie-Baxter [A. B. D. Cassie, S. Baxter, S. Trans, Faraday Soc. 40(1944)546], proposing that air is trapped between the rough surface and water drop and the shape of water drop placed on the air increases the contact angle.
Thus, in order to prepare a hydrophobic or superhydrophobic surface, a surface layer with chemically low surface energy should be formed and surface roughness should exist concurrently. It is suggested that for the surface roughness, distribution of fine pillar or pore size plays a considerably important role. Especially, a structure like a lotus leaf having nano sized roughness on micro sized roughness is suggested. It is reported that on the lotus leaf, both micro scale pillars (bump) and nanometer scale pillars (nanopillar) exist and at the same time, a chemical like wax having low surface energy is distributed to maintain its superhydrophobicity. In addition, recessed pore like structure well as this prominent shaped roughness shows similar features. Especially, when the pore size is hybrid of nano and micro scale and chemical composition of the surface is adjusted, it is possible to form hydrophobic, further even superhydrophobic surface.